The present invention relates to a variable valve timing control apparatus of an internal combustion engine, which is a variable valve system that variably controls open/close timing of an intake valve and/or an exhaust valve of the engine through a phase control mechanism by an electric motor.
In recent years, there have been proposed and developed various variable valve systems, which variably control valve open and closure timings and a valve lift amount of engine intake/exhaust valves in accordance with an engine operating state. One such variable valve system has been disclosed in Japanese Patent Provisional Publication No. 11-141314 (hereinafter is referred to as “JP11-141314”).
In JP11-141314, a variable valve system has both a variable valve timing mechanism and a variable valve lift mechanism, and a stator of an electric motor is linked to a timing pulley whose rotation is driven by an engine crankshaft, and a rotor of the electric motor is connected with a camshaft through a change mechanism. This camshaft is provided with a driving cam whose outer circumferential surface is tapered.
When a control unit (ECU) applies power to a coil of the electric motor, a motor shaft rotates, then the camshaft rotates relative to the timing pulley through the change mechanism, also the camshaft moves in an axial direction. With this mechanism, for instance, both of the valve timing and the valve lift amount of the engine intake valve are variably controlled in accordance with the engine operating state.